I have a 3 phase ESS system consisting of 3 x Multiplus II-48/8000, and a 54kWh battery with JK BMS. I have commissioned it about 4 weeks ago, and from the start observed strange behaviour on the Multiplus in phase L2. When load on AC was low, it worked well, but when load increased the power delivered by the Multiplus on L2 was jumping / oscillating. Also, the power delivered by the Multiplus on L2, as shown on the Cerbo, was delivered on the output, and just a few Watts on the input, while on L1 and L3 this was the other way around (which is correct). Note that in my setup the system should in fact deliver most load via its inputs, and just a small load on its output.
At first, I thought I had the wiring on input and output mixed, but this was not the case. Also, I thought it could have something to do with the AC cabling which was 6mm2 and 100m long. So I have doubled the cabling on the AC input to 2 x 6mm2 (100m), which did not solve the issue.
After searching on forums for weeks, and trying multiple different settings in ESS / Grid feed in settings, I finally found an old post about the external current sensor connector on the Multiplus II. It seems that on some of the newer Multiplus II models, the jack input of the external current sensor is faulty. If that is the case, the Multiplus seems to think that an external current sensor is connected, and that the power delivered to AC in is 0. While in fact it is not. That is why it shows that the power is delivered on the output (negative !), and is probably the reason for its strange behaviour. The solution is to take a 3,5mm jack plug, such as on a cheap headphones set. Plug it in to the jack on the Multiplus a couple of times, and that should solve the issue. For me, it did, and now the Multiplus shows normal behaviour; the power indications on input and output are normal now, and also the oscilating behaviour has disappeared.
It took me 4 weeks to finally find this solution in an old forum, so with this post I hope that other people will be able to find it sooner.
